In my (admittedly limited) understanding of software development, continuously developed and parallel branches aren't free. If you split up development between two different release branches, even where the code or art being worked on is compatible with both, there will eventually be some form of divergence (most likely bugs and their patches) that makes the two branches as individually labor-intensive as the project itself was before the fork. Unless you mean having a fixed version that doesn't receive updates, like the DirectX 9-10 versions.
What you said at the bottom is what i mean. It should receive updates but minor ones like bug fixes and small new features as well as new cars etc most development time should go to the performance version
